C++ gives different outputs for almost the same code - c++

Question

I have some lines of a book shuffled and their words are shuffled too. I want to sort them using quicksort algorithm. I sorted the lines and it worked well. then I tried to sort each line like this;
for each (Line l in lines) {
srand(255);
l.quicksort(0, l.words.size() - 1);
for each (Word w in l.words)
cout << w.content << " ";
cout << endl;
}
srand part is because I am using randomized quick sort. This loop gives me the correct results. However, when I tried to write it again like this;
for each (Line l in lines) {
for each (Word w in l.words)
cout << w.content << " ";
cout << endl;
}
It gives an output like I didn't call the quicksort function. It is the same code with one line missing. Why is it happening?
Line class:
#include<iostream>
#include<vector>
#include "word.h"
using namespace std;
class Line {
public:
vector<Word> words;
Line(string&, string&);
void quicksort(int, int);
private:
int partition(int, int);
void swap(int, int);
};
Line::Line(string& _words, string& orders) {
// Reading words and orders, it works well.
}
void Line::quicksort(int p, int r) {
if (p < r) {
int q = partition(p, r);
quicksort(p, q - 1);
quicksort(q + 1, r);
}
}
int Line::partition(int p, int r) {
int random = rand() % (r - p + 1) + p;
swap(r, random);
int x = words[r].order;
int i = p - 1;
for (int j = p; j < r; j++)
if (words[j].order <= x) {
i++;
swap(i, j);
}
swap(i + 1, r);
return i + 1;
}
void Line::swap(int i, int j) {
if (i != j) {
Word temp = words[j];
words[j] = words[i];
words[i] = temp;
}
}

Answer 1

You sort a local copy, iterate by reference instead:
srand(255); // Call it only once (probably in main)
for (Line& l : lines) {
l.quicksort(0, l.words.size() - 1);
for (const Word& w : l.words)
std::cout << w.content << " ";
std::cout << std::endl;
}
// Second loop
for (const Line& l : lines) {
for (const Word& w : l.words)
std::cout << w.content << " ";
std::cout << std::endl;
}